Heat barrier composition

ABSTRACT

A HEAT BARRIER COMPRISING A BONDED INITIMATE ADMIXTURE OF ALKALINE EARTH METAL SULFATE AND FINELY DIVIDED CARBONACEOUS MATERIAL PROVIDING SOURCE OF AVAILABLE CARBON, SAID BARRIER HAVING A SURFACE COATING COMPRISING ALKALINE EARTH METAL SULFIDE, FORMED BY IN SITU REACTION OF ALKALINE EARTH METAL SULFATE AND CARBON UNDER THE INFLUENCE OF HEAT WHICH RESTRICTS TRANSFER OF THERMAL ENERGY.

United States Patent No. 156,993 Int. 'Cl. C08j N30 US. Cl. 252-62 18Claims ABSTRACT OF THE DISCLOSURE A heat barrier comprising a bondedintimate admixture of alkaline earth metal sulfate and finely dividedcarbonaceous material providing a source of available carbon, saidbarrier having a surface coating comprising alkaline earth metalsulfide, formed by in situ reaction of alkaline earth metal sulfate andcarbon under the influence of heat, which restricts transfer of thermalenergy.

This application is a continuation-in-part of my application filed Sept.30, 1968, Ser. No. 763,967, now abandoned, entitled Heat BarrierComposition, which in turn is a continuation-in-part of my applicationfiled Mar. 14, 1968, Ser. No. 713,231, now abandoned, entitled GypsumPhenolic Sphere Composition.

.This invention relates to the production and use of a heat barrierproduct having a surface coating which is effective to restrict thetransmission of thermal energy.

It is an object of this invention to produce a heat barrier productwhich may be either formed as a block, sheet or other suitable formdepending upon the particular application and which is so formed that itmay be applied directly to any surface or used under any condition whereit is the desire to protect against heat transmission.

It is another object of this invention to produce an insulating materialwhich may be of low density and which has high heat barriercharacteristics resulting from the formation in situ upon the surface ofthat material of an alkaline earth sulfide which as formed provides avery effective heat barrier which either reflects or disperses heatproducing energy and thus inhibits the transmission of heat through thematerial.

It is another object of this invention to provide a heat barrier productwhich is composed of an intimate mixture of alkaline earth sulfates andfinely divided carbonaceous material which sets and which exhibits underthe application of high temperature conditions the prop erty ofproducing a heat barrier upon the surface which acts to reject orreflect heat-producing energy and which avoids or prevents to aconsiderable degree transmission of heat through the composition asformed and also is effective upon its formation in retarding the erosionof the composition under such conditions.

It is another object of this invention to provide a heat barrier productwherein the rigidity of the product formed is controlled by selectingthe materials forming the product in such manner as to permit theformation of a flexible composition which still retains thecharacteristics of providing an effective heat barrier.

It has heretofore been suggested that lightweight aggregates for plasterwalls may be prepared by mixing phenolic resin as powder, granules, orMicroballoons with gypsum plaster and that when so used the phenolicresin acts as a replacement for such other lightweight aggregatematerials such as perlite. For example, see the patent to Veatch et al.No. 2,797,201.

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I have discovered that an effective heat barrier can be produced in situupon the surface of a composition consisting essentially of an intimateadmixture of alkaline earth sulfates and finely divided carbonaceousmaterial. Upon application of heat to a surface of such a composition,the alkaline earth metal sulfate and carbon react, primarily at thesurface of the composition, whereby the sulfates are reduced to sulfidesto provide an effective thermal barrier on such surface.

Sulfides of the character here under consideration and their formationand uses are best exemplified by the article by John M. Blocher, Jr.appearing in High-Temperature Technology, Editor-in-Chief I. E.Campbell, published by John Wiley & Sons, Inc., New York and Chapman &Hall, Limited, London, as sponsored by The Electrochemical Society, Inc.of New York, wherein pages 187 to 205 set forth what is apparently thebest knowledge with respect to the formation and uses of such sulfidesand at the same time states that these sulfides, viewed as refractorysulfides for the most part, are to be considered as laboratorycuriosities.

I have further discovered that upon the formation of such sulfides uponthe surface of an alkaline earth metal sulfate composition containingcarbonaceous material, such as carbon-containing plastics, whichdecompose to active carbon upon application of sufiicient heat, heatpenetration into the composition is so reduced as to effectively retardor prevent further decomposition of the carbonaceous material therebyretarding or preventing further reduction of the sulfates to thesulfides so that erosion of the material upon such application of heatis effectively controlled.

I have also discovered that the alkaline earth sulfide coating formedupon the surface of my products is so eflective as a heat barrier thateven under application of extreme heat thereto by are plasma jet flames,heat penetration into the body of the product is inhibited to such adegree that the back surface layer of the coated product does not risematerially in temperature.

I have also discovered that the formation of the alkaline earth sulfidecoating upon the surface of such products where oxyacetylene gas torchflames are applied directly to such surface results in the same apparentrestriction of the heat flow into the material. I have also found thatthe same results are accomplished through application of any other hightemperature conditions applied to the surface such, for example, as areexistent in the exhaust at the firing of rocket engines or the like.

I have further found that the formation of the sulfide coating is asurface condition in that the material is not seriously eroded duringsuch application of high temperature to its surface due, I believe, tothe fact that when the sulfides are formed upon the surface they act toeither reflect or disperse the heat producing energy so that the heatflow into the composition is at such a rate that the temperature of thematerial underlying such sulfide surface does not rise to the point thatfurther sulfides are formed thereunder.

The compositions of my invention may be formed by using calcinedalkaline earth sulfates, i.e., those sulfates which are not fullyhydrated. The sulfates may be mixed with water to form a slurry to whichcarbonaceous material in the condition of fine subdivision is added andthoroughly admixed. The mixture is allowed to set due to hydration ofthe alkaline earth sulfates so that there is formed a composition inwhich the alkaline earth sulfates crystals form a matrix in which theparticles of finely divided carbonaceous material are held in intimatemixture therewith. The composition, before setting, can be formed intosheets or blocks or can be applied directly to the surface to beprotected from heat. When high temperature is applied thereto, thereresults the formation upon the surface of an alkaline earth sulfide dueto the reduction of the sulfate to the sulfide by the carbon which isavailable at such surface.

The term high temperature as used herein means a temperature in theorder of 900 C. or greater, i.e. at least that temperature at which thesulfates react with carbon to form sulfides.

The sulfide forms an apparent thin layer or coating upon the surface ofthe composition. Under conditions where the flame temperature applied tothe surface is approximately 10,000" E, it has been found that the backtemperature away from the flame, in a composition of /2 inch thicknessand where the continued application of the flame through the saidsurface is for a period of twenty-four seconds, has reached atemperature no higher than about 140 F. The sulfide barrier formed uponthe surface also acts by its property of restriction of heat flow to soreduce heat transmission into the material that the formation of furthersulfides is retarded in the composition as will "be demonstrated by thetest data hereinafter set forth.

The alkaline earth sulfates which are applicable for use in carrying outmy invention include magnesium sulfate, calcium sulfate, strontiumsulfate, barium sulfate, and all of the alkaline earth sulfates ofPeriodic Table 2-A as well as mixtures of any of these sulfates.

The carbonaceous materials which are useful for carrying out myinvention include all materials which will provide available carbonunder the influence of suflicient heat to effect the reaction of carbonwith sulfates according to the representative equation:

where M is an alkaline earth metal.

These materials include all forms of free carbon, such as carbon black,charcoal, coke, and graphite as well as those materials which willdecompose, coke or char under the influence of heat to produce availablecarbon. The latter materials include carbonaceous materials of naturalorigin, such as, coal, tars, pitches, asphalts, sawdust, nutshells, andother wood or vegetable wastes, natural rubber, gums and resins andmaterials of synthetic origin including substantially all of thecarbon-containing synthetic resins. The carbonaceous materials may beemployed in the form of particles which are already of small size orwhich have been reduced in size by comminuting or by process ofmanufacture. Mixtures of the various carbonaceous materials may be usedas desired. One class of suitable materials is that known under thetrademark Microballoons as disclosed in Pat. No. 2,797,201. Thecarbonaceous material may be any of the heat-decomposable film-formingmaterials, disclosed in this patent including cellulose derivatives,such as cellulose acetate, cellulose acetate-butyrate, and celluloseacetate-propionate, thermoplastic synthetic resins, such as polyvinylresins, i.e., polyvinyl alcohol (wateror organic solventsoluble),polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate,polyvinyl butyral, polystyrene, polyvinylidene chloride, acrylic resinssuch as polymethyl methacrylate, polyallyl, polyethylene, and polyamide(nylon) resins, and thermo-setting resins, such as alkyd,phenol-formaldehyde, urea-formaldehyde and melamineformaldehyde resins,natural film-forming materials including soybean protein, zein protein,alginates, and cellulose.

It is important that the carbonaceous material be finely divided inorder that it may be intimately dispersed in the alkaline earth metalsulfate so that carbon is available at substantially all points over thesurfce area of product composition, whereupon application of heat tosuch surface will provide a substantially complete coating of alkalimetal sulfide over such surface with exclusion of uncoated portionswhich might otherwise destroy the effectiveness of the product materialas a heat barrier. In general. the carbonaceous material should have amaximum average particle size below about 500 microns and, inparticular, where hollow spheres of film-forming materials are used theparticle size should be below about 500 microns not only to provide thenecessary available carbon over the entire surface area but to avoidformation of surface irregularities and holes due to melting orcollapsing of the spheres under the influence of heat. Thus, whereMicroballoons such as those described in Pat. No. 2,797,201 are used asa source of carbonaceous material, they should have an average diameterof about 1 to 500 microns, preferably 1 to 250 microns.

The proportions of carbonaceous material to alkaline earth sulfate maybe varied depending upon the conditions of application or use desired,the nature of the particular carbonaceous material used, the strengthand/ or flexibility of the desired product, and the like. The optimumamount of each carbonaceous material necessary to give the desiredsulfide coating is readily determined by simple experimentation. Iprefer to use about 0.1 to 5 parts by volume of carbonaceous material to1 part by volume of alkaline earth metal sulfate.

The application of heat to the surface of my heat barrier materials maybe from any source which will provide a temperature suflicient to causethe reaction between the alkaline earth metal sulfate and carbon. Forexample, the heat may be from an electrical source, nuclear energysource, or may be provided by a flame. Flames of reducing, neutral oroxidizing nature will cause the reaction to occur. The reaction betweensulfate and carbon occurs at a temperature of about 900 C. Continuedheating at higher temperatures may cause some reaction between alkalineearth metal sulfide and sulfate to form alkaline earth metal oxide.However, the presence of some oxide in the sulfide surface coating isnot detrimental and is considered within the scope of my invention.

Where organic material other than free carbon is used, my theory of theoperation performed under the conditions stated is that the carbonaceousmaterial chars at its temperature of decomposition leaving primarilycarbon in intimate mixture with the sulfate. Ordinarily the water ofcrystallization of hydrated sulfates is dissipated before or at thedecomposition temperature. Upon decomposition and further application ofheat the carbon acts as a reduccing agent to reduce the alkaline earthsulfate to the sulfide as a surface condition upon the composition. Thisformation of alkaline earth sulfides on the surface is as a thin filmwhich appears under the influence of the heat conditions above set forthto be in the nature of a layer which is adherent to the composition andacts either by heat producing energy reflection or dispersion as abarrier which reduces to a high degree the transmission of the heatfurther into the material or composition. The surface condition havingbeen formed, further heat transmission into the composition is inhibitedso that further charring of the carbonaceous material is slowed down asis further reduction of the sulfate to the sulfide.

I have found under these conditions that the strength of the compositionunderlying the surface is not materially affected. Under the conditionsas hereinabove expressed where a flame of approximately 10,000" F. isapplied to the surface for twenty-four seconds upon a composition of /2inch thickness, the surface erosion of the composition was found to bein the neighborhood of 0.199 and as previously set forth the backsurface temperature of the /2 inch thickness of material had reached atemperature of only in the neighborhood of F.

I have further discovered that I am able to control the flexibility ofthe composition of my invention by, in effect, interrupting thecrystalline interlock of the alkaline earth sulfates forming thecomposition by adding to the composition of alkaline earth sulfates,thermoplastic carbonaceous materials such as the thermoplastic vinyl,styrene, acrylic, cellulosic, olefinic, and nylon polymers andcopolymers, so that I am able to produce a flexible composition asdistinguished from a hard inflexible material without interfering withthe fundamental property of forming the sulfide upon the surface thereonunder conditions of heat application as hereinabove set forth.Thermoplastics such as the polyvinyl alcohols and polyvinyl acetates maybe dissolved or suspended in the water used to form the alkaline earthmetal sulfate slurry. Mixtures of the various carbonaceous materialsboth thermosetting and thermoplastic may be used. The formation of thecomposition having flexible as distinguished from rigid characteristicsenables the composition to be used and applied under conditions whererigidity of the composition would deter its application.

I have further found that in the preparation of the compositionembodying my invention that I am able to produce the composition in suchmanner as to avoid the formation of cracks or fissures in the materialupon the conditions of application of high temperature to its surface ashereinabove defined by incorporating in the slurry formed of the alkaliearth sulfates and carbonaceous material a strain or grid of fiber glasseither at the surface or embedded in the composition as it is allowed toset.

The following are set forth as specific examples of the compositionembodying my invention and of the test results observed.

EXAMPLE I Calcium sulfate, i.e., calcium sulfate hemihydrate (CaSO /2HO) is mixed with water to form a slurry using the same proportions ofcalcium sulfate hernihydrate and water as is ordinarily used in forminga slurry for casting purposes. The slurry thus formed as allowed tostand for such period of time as will permit the addition thereto ofphenolic resin either in finely ground condition or as Microballoonswithout the tendency of the said phenolic resin to separate during thesubsequent setting, which thereby forms a matrix holding the phenolicresin intimately dispersed with the calcium sulfate throughout thecomposition. In this composition I employ in this specific example 30%by volume of CaSO /2H O and 70% by volume of finely divided phenolicresin of 500 micron maximum average particle size and the amount ofwater added to form the slurry is in accordance with good practice thatamount which will permit the formation of a thick cream slurry, i.e., inmost cases employing the minimum of water which will permit theformation of a uniform intimate mixture of the CaSO /zI-I O and phenolicresin. The ratio of CaS0 /2H O, phenolic resin and water employed informing the composition may, of course, be varied depending upon theconditions of application or use desired and is not herein set forth asa limitation of the proportions of ingredients used in carrying out myinvention.

I have similarly prepared compositions employing magnesium sulfate,strontium sulfate, and barium sulfate, and phenolic resin, and others ofthe carbonaceous plastics.

EXAMPLE II In producing the composition embodying m invention so that itwill have flexibility as distinguished from rigid compositions producedby the above set forth example, I have in a similar manner produced theslurry of the alkaline earth sulfate and water and thermosetting plasticand have added thereto a suspension of thermoplastic material and havefound that the composition thereby produced is flexible as distinguishedfrom a rigid composition. Specifically, I have mixed 100 parts by volumeof CaSO /2 H O, sufiicient water to form the slurry as above described,to which I have added 200 parts by volume of phenolic resin, and 100parts by volume of the approximately 50% suspension of polyvinyl acetatein water and have found that upon setting, the resultant composition wasflexible as distinguished from the rigid composition produced by thefirst stated example. The operation ap parently performed in thisexample is that the addition of the vinyl plastics to the composition inexcess of that set forth in the first example given has prevented thecomplete interlock of the crystals of the alkaline earth sulfate,leaving the composition flexible.

HEAT-BARRIER TESTS A test block of the composition was prepared in themanner hereinabove set forth in Example I in which proportions were 70%by volume of phenolic resin Microballoons (max. average particle size500) to 30% by -volume of CaSO /zH O with water which was allowed to setto form test blocks which were 2" x 2" square and of /2" thickness. Anarc plasma jet flame was applied to the surface of such block under thefollowing conditions:

Heat flux (B.t.u./ft. -second) 1000 Gas enthalpy -(B.t.u./lb.) 6050 Testduration in seconds 24 Stagnation pressure (p.s.i.g.) 1.242 Gastemperature F.) 10025 Gas velocity (ft/second) 1913 with the followingresults:

Further tests were conducted in blocks of the same composition todetermine the rate of erosion of the surface with the following results:

Test time (500.)

Erosion rate Specimen (mil/sec.)

Further tests Were conducted employing larger sheets of the samecomposition of like thickness which were tested in an oven over propanegas burners which were spaced 18" on center and where the burners wereplaced 30" from the face of the test panel. Propane gas was burned inthe burners under the conditions hereinafter set forth. The temperaturesat the face of the panel, toward which the flames were directed weremeasured by means of eight Chromel-Alumel thermocouples encased in /2inch iron pipe and placed approximately 6" from the panel face. Thevertical and lateral placement of the thermocouples was determined byexperimentation and visual observation of the flow pattern of theburning gases. Thermocouple leads were connected through a rotary switchto a Techniques Associates Pyrotemp Model 9-B pyrometer from whichtemperature readings were obtained manually. The backside temperatureswere taken by placing seven iron-constantan thermocouples on the crossframing of the panel and with one thermocouple placed directly on theback surface of the composition. The following temperature readings indegrees Fahrenheit were taken from the panel face:

Temperature readings, degrees F., panel face Station number Requiredtemp.

""" "at"'a asa sss ba"at;

The pressure of the gas flowing to the burners at the start of the testwas five pounds per. square inch which was increased to ten pounds persquare inch after five 7 minutes at which gas pressure the test wascontinued for the full duration of twelve minutes.

The temperatures at the back of the panel measured by the thermocouplesas above described were as shown by the following table:

Temperature readings, degrees F., panel hack Min. Max.

10 Minutes:

Further tests utilizing substantially the same equipment and testsamples of the same character have been conducted wherein for a totalelapsed time of two hours and fifteen minutes the average surfacetemperatures taken over the hot side surface have been in excess of 1900F. and the temperature of the back face taken likewise over Other formsof carbon, such as carbon black, pulverized charcoal and finely dividedgraphite may be substituted for coal in the above formula. The glassfibers and polyvinyl acetate may be omitted if high strength andflexibility is not necessary for the particular use. Other sulfates,such as barium sulfate, may be substituted for part or all of thecalcium sulfate. Other polymers may be included as solutions ordispersions in the liquid phase to impart the special characteristics ofthese polymers. It will be understood that emulsifiers and dispersantsas well as antifoaming agents may be included as desired.

PARTICLE SIZE In order to illustrate the importance of particle size ofcarbonaceous materials the following samples were prepared and tested:

These materials were mixed with Water and cast into 3" x 3" x 1" testsamples. After the samples had set they were subjected to a flameprovided by an oxy-acetylene torch. The tip of the torch wasapproximately five inches from the sample surface and the torch wasadjusted to provide a slight excess of oxygen. The condition andbrightness of the surface of the material during the test was recordedphotographically. Sample 8, which contained no carbonaceous additive,was taken as the control sample.

The samples containing the larger size particles exhibited severesurface erosion when exposed to the flame. The surface brightness of thecontrol sample 8 was given a value of 1 and the relative brightness ofthe surface of the other samples was measured against this controlvalue. Samples 1 and 2 had a relative surface brightness of about 32 and64, respectively, representing a high surface reflectivity due to theformation of a uniform sulfide and/or oxide coating on the surface.Sample 5 showed substantially no increase in surface brightness over thecontrol and samples 6 and 7 had a relative surface brightness of about2. The relative surface brightness of samples 3 and 4 was intermediatebetween that of samples 6 and 7 and sample 1. On the basis of thesetests I conclude that the maximum average particle size of carbonaceousmaterial which will provide beneficial results pursuant to the presentinvention is about 500 microns. Samples 1-4 are representative exampleswithin the scope of the invention. Samples 5 through 7 constituterepresentative examples where the average particle sizes are reduced tono greater than about 500 microns.

In order to account for the unexpected results, i.e., the formation ofthe thin adherent heat restrictive sulfide on the surface, and the factthat this material under these conditions exhibits these unusualproperties of what I term heat rejection, I have endeavored to determineas nearly as possible the phenomena occurring under the conditions asset forth. It appears fundamentally that the reaction which is occurringunder the influence of the heat application to the surface is that thecalcium sulfate is reduced to calcium sulfide principally through theaction of chemically active carbon in intimate contact with the sulfate.When this contact is maintained under the heat conditions defined thereis a direct reduction to the sulfide principally through the formationof carbon dioxide liberated from the surface after or perhapssimultaneously with the formation and liberation from the material ofwater in the form of steam and the formation of some carbon monoxide andtraces of what I am unable to explain of methane (CH which is found byanalysis of the gas leaving the surface of the material under theconditions hereinabove defined, indicating that there is present underthe conditions of these tests an excess of reducing capacity. Theprimary reaction may be, in a somewhat simplified form, indicated by thefollowmg:

(Phenolic Resin) (Gypsum) IOCaS 32H 0 16 00 40 (Calcium Sulfide) C OHydrocarbon (trace) (trace) No attempt has been made to balance theabove equation; this for the reason that depending upon the period oftime that a gas analysis is made of the gases leaving the surface, theproportions of carbon dioxide, carbon monoxide, water and methane willobviously vary.

It has been found that upon the cooling of the composition after theformation of the calcium sulfide barrier upon its surface where thecooling has been permitted to take place in the atmosphere that theremay be some deterioriation of the adherent calcium sulfide layer uponthe surface apparently due to its reaction with the water of the airresulting in the formation upon the surface of calcium oxide and calciumhydroxide along with some residual calcium sulfide depending upon theperiod of time when the observation is made. The material thus remainingupon the surface after exposure to the water in the air is a whitepowdery material and this material is no longer tightly adherent to thesurface. The change in the surface condition which takes place whenexposed to the water of the atmosphere has been found,

however, to have no appreciable effect upon the heat barrier propertiesof the composition embodying my invention. When the surface of suchcomposition is subjected to like heat conditions as hereinabove setforth the thin adherent coating of alkaline earth sulfide will againform upon the surface of the composition forming the same heat barriercharacteristics hereinabove defined.

Having fully described my invention it is to be understood that I do notWish to be limited to the details here* inabove set forth. My inventionis of the full scope of the appended claims.

What is claimed is:

1. -A heat barrier comprising a bonded, intimate admixture of alkalineearth metal sulfate and finely divided carbonaceous material having amaximum average particle size below about 500 microns, said barrierhaving a substantially continuous surface coating consisting essentiallyof alkaline earth metal sulfide.

2. The heat barrier of claim 1 wherein the surface coating of alkalineearth metal sulfide is formed by in situ reaction of alkaline earthmetal sulfate and carbon, provided by said carbonaceous material, underthe influence of heat.

3. The heat barrier of claim 1 wherein the carbonaceous material in theadmixture comprises free carbon.

4. The heat barrier of claim 1 wherein the carbonaceous materialcomprises a carbon-containing material which will char or coke under theinfluence of heat to provide available carbon.

5. The heat barrier of claim 1 wherein the carbonaceous materialcomprises a thermosetting plastic.

6. The heat barrier of claim 5 wherein the thermosetting plastic is aphenolic resin.

7. The heat barrier of claim 6 wherein the phenolic resin is in the formof Microballoons.

8. The heat barrier of claim 7 wherein the ratio of phenolicMicroballoons to the alkaline earth sulfate by volume is in the order ofabout 7 to 3.

9. The heat barrier of claim 1 wherein the volume ratio of carbonaceousmaterial to alkaline earth sulfate is in the range of about 0.1 to 5parts by volume of carbonaceous material to 1 part by volume of alkalineearth sulfate.

10. The heat barrier of claim 1 wherein the admixture includes athermoplastic material which increases the flexibility of said barrier.

11. The heat barrier of claim 1 wherein the admixture includes a fibrousmaterial which resists the formation of fissures or cracks in thebarrier during application of heat thereto.

12. The heat barrier of claim 11 wherein said fibrous material comprisesglass fibers.

13. The heat barrier of claim 1 wherein the carbonaceous materialcomprises microspheres of a film-forming resin and a water-soluble ordispersible thermoplastic resin deposited within the barrier compositionfrom a liquid carrier.

14. The heat barrier of claim 1 wherein the carbonaceous materialcomprises coal and a water soluble or dispersible thermoplastic resindeposited within the barrier composition from a liquid carrier.

15. The heat barrier of claim 1 wherein the alkaline earth metal sulfatecomprises calcium sulfate.

16. The heat barrier of claim 1 wherein the alkaline earth metal sulfatecomprises barium sulfate.

17. The heat barrier of claim 1 wherein the alkaline earth metal sulfatecomprises magnesium sulfate.

18. The heat barrier of claim 1 wherein the alkaline earth metal sulfatecomprises strontium sulfate.

References Cited UNITED STATES PATENTS 2,797,201 6/ 1957 Veatch et a1.2602.5 B 3,104,196 9/1963 Shannon 260---2.5 B 3,214,393 10/ 1965 Sefton2602.5 B 3,257,338 6/1966 Sefton 2602.5 13 3,272,765 9/1966 SeftOn2602.5 B

MURRAY TILLMAN, Primary Examiner M. FOELAK, Assistant Examiner US. Cl.X.R.

